The invention relates to a surgical laser instrument for the alternate contact cutting and no-contact coagulating of biological tissue by means of a fiber-optically guided irradiation of a laser which, for this purpose, is connected with a fiber-optic light guide as the cutting and coagulation instrument.
In laser surgery, contact cutting is frequently preferred over no-contact cutting because it is difficult to guide the fiber-optic instrument at a uniform distance above the tissue. In addition, in the case of the previous laser systems, it is essential that the optical fiber not be brought in contact with the tissue during the irradiation because the tissue residues adhering to the fiber immediately burn into the fiber and ultimately lead to an overheating and breakage of the fiber. For this reason, a surgical laser instrument is suggested in the U.S. Pat. No. 4,693,244 which, for the purpose of contact cutting, carries a sapphire tip at the end of an optical fiber which better withstands thermal stress during contact cutting. These sapphire tips which have already been introduced into laser surgery, however, are relatively expensive and expediently are suitable only for cutting. In addition, the service life of sapphire tips of this type is limited and is drastically reduced in the case of improper handling. Finally, it is difficult to achieve a targeted coagulation under constant visual control of the respective irradiated patch of tissue.
It is therefore an object of the invention to provide a surgical laser instrument for the alternate contact cutting and no-contact coagulating of biological tissue by means of a fiber-optically guided irradiation of a laser which provides high technical safety requirements, particularly with respect to the service life of the fiber-optic light guide, and at the same time permits more diverse work than by means of the known instrument.
This object is achieved by means of a surgical laser instrument according to the invention in which the light emitted in the visible spectral region between 0.3 and 0.9 .mu.m ("white light"), due to pyrolytic glowing of biological tissue which has been at least partially carbonized due to the impinging laser radiation, is detected and is used for controlling the output of the laser. In this case, the term "fiber-optic light guide" applies to all components which guide the laser light to the tissue to be treated, so that this protection applies to the use of the naked fiber as a cutting and coagulation instrument as well as to those fiber-optic light guides in which an applicator is made of an at least partially optically transparent material, such as a sapphire tip, coupled to the distal end of the optical fiber.
An arrangement for the laser treatment of tissue is disclosed in German Patent document DE 38 13 918 A1, in which a sensor detects the fluorescent radiation originating from the treated tissue as a result of the impinging laser radiation, and permits an identification of the tissue by means of a spectral analysis unit. Because of this information, the laser irradiation may be optimized. However, the objects of the present invention cannot be achieved in this manner, particularly since the fluorescent radiation emitted by the tissue does not furnish any clear information with respect to the thermal stressing of the light guide. By contrast, the Laser surgical instrument according to the invention detects the carbonization of the biological tissue (and hence, the direct thermal stressing of the fiber during the carbonization of the tissue residues adhering to the distal end of the fiber), and by controlling the laser output, ensures that the destruction threshold of the light guide material is not exceeded. Uniform contact cutting in the tissue is thus achieved.
If, after the contact cutting, certain tissue parts are to be coagulated in a no-contact manner, it is sufficient to pull the light guide contaminated by tissue residue out of the incision and to hold it in front of the tissue area to be coagulated at a distance that can be observed well. Since the radiation that previously had been emitted mainly by the tissue to be cut is now absent, the radiation output of the laser is increased until the tissue residues on the light guide re completely carbonized and burned up. The resulting irradiation therefore reaches a predetermined value which represents the destruction threshold of the light guide. The fiber end will then become increasingly more transparent for the laser radiation so that the laser is controlled upward to a predetermined output limit, and may then be used for the coagulating with a sufficient distance between the fiber end and the tissue. Surprisingly, the invention therefore solves several problems so that, in contrast to prior art devices, an alternate contact cutting as well as a no-contact coagulating becomes possible even by means of the bare fiber while the service life is prolonged.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.